According to conventional methods, an enhancement level of high-frequency enhancement processing is set up corresponding to the largeness of value based on the benchmark which indicates unevenness (scattering) of pixels of an attention area. However, even when degrees of variability of pixels relative to the attention pixels are the same, the larger the pixel value is, the larger the absolute value of variation trends to be, and reversely the smaller the pixel value is, the smaller the absolute value of variation trends to be, with regard to unevenness of pixels in general. Specifically, with regard to the benchmark value of unevenness (dispersion), the larger brightness value is, the larger the benchmark value trends to be, and reversely the smaller brightness value is, the smaller the benchmark value trends to be.
Therefore, given a corresponding relationship is set up to meet a characteristic when the brightness value is large, an unevenness, of which brightness value is small, becomes undetectable, so that the benchmark value becomes small and consequently, the enhancement level set-up corresponding thereto cannot be correctly set up. Further, in contrast, when given a corresponding relationship is set up to meet a characteristic when the brightness value is small, an unevenness, of which brightness value is large, is overly detected, so that the benchmark value becomes large and consequently, the enhancement level set-up corresponding thereto is strongly set up. As results, it is problematic that given the corresponding relationship is set up to meet the characteristic when the brightness value is small, the noise component is amplified, so that quality of the image deteriorates. Accordingly, the subject region is speculated based on the detected representative brightness value so that the enhancement level is set up to solve the problem as set forth above (e.g., see Patent Document 1).